The present invention relates generally to magnetic resonance (MR) imaging systems and methods. More particularly, the present invention relates to a MR imaging system equipped for real-time imaging and methods for assisting the operator to interactively prescribe the geometry of the excitation profile of a structure of interest for subsequent acquisition of a MR image of the structure of interest.
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field Bo), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but process about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is the x-y plane and which is near the Larmor frequency, the net aligned moment, Mz, may be rotated, or xe2x80x9ctippedxe2x80x9d, into the x-y plane to produce a net transverse magnetic moment M. A signal is emitted by the excited spins after the excitation signal B1 is terminated and this signal may be received and processed to form an image.
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
When attempting to define the volume of coverage of an MR imaging scan, the NMR system operator may desire to quickly view a preview MR image (such as a real-time MR image) of the anatomical section within this volume of coverage. This process can be particularly useful when prescribing a three dimensional imaging volume, in which the desired high spatial resolution requires the thinnest slab possible. It is desirable to position this thin slab such that the anatomical section within the volume of coverage is complete, i.e. for example, covers the entire desired vascular network. Thus, a quick view of each side of the slab prior to initiating the three dimensional acquisition is useful for insuring that the entire anatomical section desired is within the defined volume of coverage.
Typically, two dimensional axial, sagittal and coronal xe2x80x9cscoutxe2x80x9d images are first acquired. Such scout images are stored for later use. To use, the operator calls up the scout image and either graphically or explicitly (using geometry coordinates) prescribes the imaging volume directly on the scout images. The imaging volume may be either a two dimensional stack of slices or a three dimensional slab of the structure of interest. The drawback of this technique is that the operator does not actually see the results of the prescribed geometry until the subsequent imaging volume is acquired. Prescription errors cannot be detected nor corrected until the imaging volume acquisition is complete. Thus, when prescription errors exist, the operator is required to re-prescribe and re-acquire the imaging volume of the desired anatomical section.
One embodiment of the invention relates to a method for defining an imaging plane of an image to be acquired of a structure of interest. The method includes selecting a previously acquired three-dimensional image of the structure of interest, and determining a first geometry information associated with a first boundary plane of the previously acquired three-dimensional image. The method further includes determining a second geometry information associated with a second boundary plane of the previously acquired three-dimensional image, and selecting at least one of the first geometry information and the second geometry information to define the imaging plane. The image to be acquired is a planar image.
Another embodiment of the invention relates to a system for defining an imaging plane of an image to be acquired of a structure of interest. The system includes means for selecting a previously acquired three-dimensional image of the structure of interest, and means for determining a first geometry information associated with a first boundary plane of the previously acquired three-dimensional image. The system further includes means for determining a second geometry information associated with a second boundary plane of the previously acquired three-dimensional image, and means for selecting at least one of the first geometry information and the second geometry information to define the imaging plane. The image to be acquired is a planar image.
Still another embodiment of the invention relates to an imaging system retrieving geometry prescription information from an image volume of a structure of interest to define an imaging plane of an image to be acquired. The system includes a storage device configured to store the image volume, and an interface in communication with the storage device and configured to transmit at least one selection signal in response to an operator selecting the image volume on the interface. The system further includes a system control in communication with the storage device and the interface. The system control is configured to determine at least one of a first geometry prescription information and a second geometry prescription information associated with a first boundary plane and a second boundary plane, respectively, of the image volume. At least one of the first and second geometry prescription information defines the imaging plane of the image to be acquired.
Yet still another embodiment of the invention relates to a planar magnetic resonance (MR) image of a structure of interest provided using an MR imaging system. The image comprises an imaging plane defined by a geometry parameter associated with a boundary plane of at least one of a first previously acquired volume image of the structure of interest and a second previously acquired volume image of the structure of interest.